The present invention generally relates to a polishing device and more particularly, to a polishing spindle for use in a polishing device to be employed in a polishing/finishing process, i.e. a so-called polishing process for all kinds of lenses such as spherical lenses, aspherical lenses, etc.
Conventionally, there have been employed various kinds of polishing processes for spherical and aspherical lenses.
Particularly, in the field of optical instruments, it has been a trend in recent years that not only the spherical, but also aspherical optical glass lenses of required configurations are being used to reduce the size and weight and increase the performance of optical instruments. For example, in a toric lens to be used in a laser beam printer, a special shape is required, and the desired shape has been obtained by subjecting a workpiece which had been previously ground to a spherical shape having an approximate radius of curvature to a finish polishing process, by changing tools during processing. By way of example, for the above practice, there has been employed a known arrangement as shown in FIGS. 3(a) and 3(b) and disclosed in Japanese Patent Laid-Open Publication Tokkaisho No. 63-216664.
Hereinbelow, the above conventional polishing device will be explained with reference to a side sectional view shown in FIG. 3(a) and a front elevational view shown in FIG. 3(b) of the polishing device.
The known polishing device of FIGS. 3(a) and 3(b) is so arranged that, by attaching a workpiece 1 onto an outer periphery of a rotatable wheel 2, a female die jig 3 of iron, cast iron, stainless steel or the like formed with a concave toric surface is urged against an outer peripheral processing surface of the workpiece 1 under a predetermined force F. In the above state, an abrasive material, such as abrasive grain of green silicon carbide of #600 to #4000 and the like, is supplied between the female die jig 3 and the processing surface of the workpiece 1 while the wheel 2 is being rotated. Further, the female die jig 3 is oscillated in a direction intersecting at right angles with a rotating direction of said wheel 2. In this manner, lapping processing can be effected by successively reducing the particle size of the abrasive grain. In a finishing step, a polisher of polyurethane or the like is applied onto the female die jig 3, while grain particles of selium oxide having particle size of about 1 .mu.m are fed between the jig 3 and the processing surface for polishing in a similar manner as above. The female die jig 3 having a proper length along the workpiece 1 in the rotating direction of the wheel 2 is engaged, at opposite ends of its upper surface, with tips of a pair of depressing needles 4 so as to be supported for oscillation in a transverse direction, while also being pivotable in the longitudinal direction, since the depressing needles 4 are fixed at opposite ends of a pivot lever 5 supported for pivotal movement in a longitudinal direction of the female die jig 3. Meanwhile, the pivot lever 5 is pivotally connected to an operating arm 6 urged towards the axis of the wheel 2 and reciprocably movable in the axial direction of the wheel 2.
However, in the conventional arrangement for lapping and polishing as described above, since the direction of oscillation of the female die jig 3 is naturally the same at any position along the longitudinal direction, even if the oscillating face S is aligned with the radial direction T of the wheel 2 at the central portion, such oscillating face S will be inclined by an angle .THETA. with respect to the radial direction T of the wheel 2 at the opposite ends (FIG. 3(b)). Therefore, the curvature of the curved surface to be formed by the oscillation of the female die jig 3 is not in agreement with the toric face in terms of principle. Accordingly, in actual use of such processing method, it is very difficult to attain high accuracy of the toric surface. It is also difficult to maintain the accuracy of the toric surface for the female die jig 3, and thus, skill and "knack" are required as in manual processing to obtain high accuracy, thus resulting in very poor productivity and consequent high costs.
In order to overcome the disadvantages as described above, Japanese Patent Laid-Open Application Tokkaisho No. 63-216664 (referred to earlier) intends to solve the problem by an arrangement in which a processing point of a processing tool effects a drum-shaped locus movement with a radius of curvature equal to the radius of curvature at one side of the toric surface to be processed, to thereby achieve higher accuracy and efficiency in processing. However, in such known arrangement, the apparatus main body is complicated and requires high accuracy, and even if the arrangement is suitable as a grinding apparatus, it is not suitable as a polishing apparatus.
Meanwhile, although there has further been proposed a polishing method by an elastic member having an inner pressure, the amount of deformation of the elastic member is limited only by the control of the inner pressure, and thus, the contact area with the workpiece is undesirably varied. This results in a non-uniform depressing force per unit area, and makes it impossible to quantitatively determine the amount of processing necessary to obtain a polished surface at high accuracy.